Britain must be prepared to match the 'strategic endurance' of the Taliban in Afghanistan, a former head of the Army has warned.

General Sir Mike Jackson said that the job of nation-building in Afghanistan cannot be completed overnight, and is not anywhere near finished.

He welcomed yesterday's announcement of an additional 230 troops to improve security, train Afghan forces and assist with reconstruction, and rejected suggestions that it would significantly increase the pressure of 'overstretch' on the armed forces.

Gen Jackson said it would be wrong to put a timeframe on withdrawal from Afghanistan or Iraq.

British soldiers must be prepared to match the endurance of the Taliban in Afghanistan, a former army head has warned

British soldiers must be prepared to match the endurance of the Taliban in Afghanistan, a former army head has warned

He told BBC Radio 4's Today programme: 'In any theatre where one is seeking to move a country out of some dark past to a better future, dates are relatively unimportant.

'What you are seeking to do is to achieve the conditions within which both the country itself and those there to help it come to an agreement that all has been done that can be done.

'We are still not there in Iraq, in my judgment.

'(In Afghanistan), I don't think we are nearly there. We are certainly heading in the right direction, there is no doubt in my mind about that at all.

'We must learn that nation-building - which is what we are doing - can't be done overnight or anything that approaches it.

'We can be quite certain that our opponents have strategic endurance. We must match that strategic endurance - indeed overmatch it.'

The deployment announced yesterday will bring to 12,000 the total British commitment in its two main theatres overseas - 8,000 in Afghanistan and 4,000 in Iraq.

But Gen Jackson said this level of commitment was 'do-able in my judgment'.

'There is a total of 12,000 deployed at any one time; an Army of 100,000 can make that work,' he said.

'Let's not forget it is not that long ago that we had 20,000 soldiers stationed in Northern Ireland.'

He added: 'The Army will have taken care to make sure that this modest increase doesn't put it under any obviously greater strain.'